The present invention relates to ultrasonic imaging equipment and, in particular, to a method and apparatus providing higher quality ultrasound images by combining data from several time displaced and/or several frequency displaced images.
Ultrasonic imaging provides a mapping of ultrasonic echo signals to an image plane where the magnitude of the reflected ultrasound wave (“echo”) is mapped to brightness of pixels in the image. Such images may reveal structures within the body as delineated by the increased reflection that occurs at the interface between materials of dissimilar acoustic properties, for example, different tissue types.
Greater insight into the physical properties of the material being imaged may be obtained by using the ultrasound images for elasticity measurements. In one type of elasticity measurement termed “quasi-static elastography”, two images of a material in two different states of deformation are compared. The material may be deformed by compression with the ultrasound probe itself, for example, or by the internal muscular forces, for example the patient stretching a tendon or the beating of a heart in medical imaging. Strain is deduced from these two images by computing gradients of the relative shift of the material in the two images along the deformation axis and the elasticity is deduced from this strain with an assumption about the applied force. Elastography in medical imaging is analogous to a physician's palpation of tissue during which the physician determines stiffness by finger pressure and detects the amount of material yield (strain) under this pressure.
Multiple ultrasound images, obtained rapidly in succession at different times, can provide ultrasonic video whose time dimension offers additional insight into the material being imaged. In theory, successive frames of ultrasound video can also provide for additional spatial information, for example, by combining the data of separate images into a higher resolution image. In practice, combining ultrasonic images to produce higher-quality images has been difficult to achieve.